Much has been written on the use of observational studies in epidemiological research. It will be necessary to apply many of the same epidemiologic techniques used in conventional observational studies to the clinial data bank. Work on determining which epidemiologic approaches are most appropriate for use with clinical data banks has begun in conjunction with the Pilot Stroke and Traumatic Coma Databank Networks (N01-NS-8-2309, 6, 7, 8; N01-NS-9-2302, 96, 97, 98). The current focus of this project has been quality assurance methods for use in multicentered clinical data banks.